Delta Force, or formally 1st Special Forces Operational Detachment (SFOD) Delta, is a U.S. military counterterrorism and hostage rescue unit assigned to the Joint Special Operations Command of the United States Special Operations Command. While an Army unit, it will often have special operators from other services attached to it, especially Air Force Special Tactics and Navy SEALs.
While many Delta Force operators come from a background in the United States Army Special Forces or Rangers, Delta missions differ from both. While Special Forces do have direct action and special reconnaissance capabilities, they are especially well qualified for long-term assignments working with foreign military personnel in unconventional warfare and foreign internal defense. Rangers are direct action specialists, but usually operate in uniform. Delta Force is more apt to conduct its missions covertly.
In 1977, President Jimmy Carter sent a letter to the Joint Chiefs of Staff, asking if the U.S. had an antiterrorist capability such as the German GSG-9 unit that had conducted a hostage rescue in Mogadishu, Somalia. Edward "Shy" Meyer, then Army Vice Chief of Staff, convinced GEN Bernard Rogers, then Chief of Staff of the Army, to create such a unit; it was an Army, not joint, initiative. Meyer tasked COL Charlie Beckwith to create a "ranger/shooter" type of unit that would be formally called First Special Operations Detachment Delta (Airborne), or commonly Delta Force, the unit was consciously patterned after British Special Air Service, with whom had served an exchange tour. It also reflected Beckwith's experience with MACV-SOG.
Beckwith, in a 1973 tour with the Joint Casualty Resolution Center, had proposed such a unit to his commander, BG Robert Kingston.  In 1975, Kingston had been promoted to commander of the Special Warfare Center, while Beckwith, now a colonel, commanded the Special Warfare School. Kingston responded to inquiries from Meyer with a proposal from Beckwith, which was briefed to various senior officers, including GEN Frederick Kroesen, head of United States Army Forces Command. Some of these saw the proposed force as competition to the Rangers. He was, however, given the go-ahead in September 1977.  While SAS has an advisory and guerrilla leadership capability, it is not their primary emphasis.
Mountel, however, had developed a more general-purpose, clandestine operations and special reconnaissance subunit, called BLUE LIGHT, within his command, 5th Special Forces Group. Beckwith saw this as competing, and, when Beckwith made Rogers and Carter aware of it, BLUE LIGHT was cancelled. Mountel wrote,
It [Delta] was more a pastiche of techniques and backgrounds — some borrowed from SAS and some borrowed from the Vietnam across-the-border operations — and all blundered into a macho whole that did not square with what I thought I knew about counter-terror operations in the twentieth century.
- Operation ACID GAMBIT : During Operation Just Cause in Panama, the first full Delta Force mission, to rescue a U.S. Central Intelligence Agency asset, Kurt Muse.
- Operation DESERT STORM : That part of the Gulf War, beginning with the first air strikes at 02:00 local time, 17 January 1991, until the main ground assault into Kuwait, Operation DESERT SABRE
- Operation GOTHIC SERPENT : During United Nations operations in Somalia, a U.S. raid to capture members of Mohammed Aideed's faction; helicopters were shot down leading to the incident described in Black Hawk Down 
- Battle of Tora Bora : A battle of the Afghanistan War (2001-), in which allied special operations forces, principally using Afghan troops, attempted to kill or capture an escaping Osama bin Laden <ref name=Fury>Dalton Fury (pseud.) (2008), Kill Bin Laden: a Delta Force Commander's Account of the Hunt for the World's Most Wanted Man, St. Martin's Press, ISBN 0312384394>/ref>
- Iraq War : Invasion of Iraq by a coalition of countries, led by the United States, in 2003, and subsequent occupation
- Charlie A. Beckwith, Donald Knox (1983), Delta Force: The Army's Elite Counterterrorist Unit, HarperCollins, ISBN 0380809397, pp. 99-102
- Beckwith, pp. 126-127
- Adams, pp. 161-163
- quoted in Adams, p. 162
- Mark Bowden (2001), Black Hawk Down: A Story of Modern War, Signet, ISBN 0451203933